Question 1

If a mutagenesis screen provides some number of alleles shown by complementation analysis to be in the same gene, which of the following is true?

Accepted Answer

Mutants that are allelic (i.e., affect the same gene) can be used to study the function of that gene, including its role in metabolism.

Question 2

What kind of analysis is needed to determine whether two mutations are in the same gene or in different genes?

Accepted Answer

complementation

Question 3

Besides the obvious fact that chemical mutagens are dangerous to handle, another major disadvantage to their use is that __________.

Accepted Answer

The use of chemical mutagens can result in subtle changes to DNA that may not be immediately detectable through traditional methods like gel electrophoresis. Instead, sequencing may be necessary to identify mutations induced by chemical agents.

Question 4

To introduce dsRNA into C. elegans, it is enough just to dip the worms into media that includes E. coli containing the dsRNA because __________.

Accepted Answer

C. elegans is a bacterial feeder and can take up E. coli containing dsRNA through feeding. As the worms ingest the bacteria, they also take up the dsRNA, which can then silence the target gene expression.

Question 5

You have evidence that a gene, VTE4, of known sequence and well-understood transcriptional regulation, is available from another lab. The product of this gene enables seeds to produce a significantly increased amount of vitamin E from a substrate already produced in Brassica napus, the plant that gives us canola oil. To produce canola oil with increased vitamin E, how would you proceed?

Accepted Answer

The answer of You have evidence that a gene, VTE4,...

Question 6

If mutagenizing a number of Drosophila results in several observable phenotypes but also in several lethal mutations, does this mean that recessive lethal mutations cannot be studied further?

Accepted Answer

Even if the mutation is lethal, it can still be studied by recovering the lethal allele from heterozygous siblings.

Question 7

Before Muller's discovery that radiation induces mutation, scientists had to work on mutations that were found solely by phenotype differences in natural populations. Which of the features
Of Drosophila made it a fortuitous choice for Morgan and his colleagues?

Accepted Answer

Drosophila has a large number of easily visible phenotypes, which made it easier for Morgan and his colleagues to identify mutations and study their inheritance patterns.

Question 8

Enhancer trapping might occur if you create a library of insertions bearing enhancer-less GAL4 genes. Their expression will be controlled by __________.

Accepted Answer

Enhancer trapping occurs when a gene without enhancers is randomly inserted into the genome, and its expression is controlled by the enhancers that are present nearby in the genome. Therefore, the best choice is D, which suggests including enhancers that map near the insertion site. Adding a viral enhancer or enhancer activator might increase the expression levels but would not necessarily trap enhancers. Including a GAL4 reporter or bacterial origin sequence is not relevant to enhancer trapping.

Question 9

Identifying an autosomal recessive mutation in a mutagenic screen in Drosophila requires identification of a mutant in the F₃ generation. If testing for a sex-linked recessive lethal mutation (e.g., cn l + using a balancer chromosome such as cnCyO), in which generation can lines with mutations be identified?

Accepted Answer

The answer of Identifying an autosomal recessive mutation in a...

Question 10

If a gene in Drosophila is expressed only when an imaginal disc (A)begins to differentiate, it is referred to as a homeotic gene. Recessive mutations in such genes often result in loss of function so that the structure does not develop. If the gene is expressed, but in a different imaginal disc (B), what is the result?

Accepted Answer

If the gene is expressed in a different imaginal disc, it may cause the gene to be active at the “wrong” location, resulting in a gain of function in disc B. This can lead to the development of structures in disc B that would not typically be present or a change in the structure of disc B. However, it would not lead to loss of function in disc B's primary gene or deregulation of gene expression throughout disc A or B.

Question 11

Which of the following would make a human disorder-causing allele or gene easiest to locate?

Accepted Answer

A single patient with a chromosomal translocation associated with the gene would provide a clear starting point for mapping the location of the gene. By identifying the breakpoints of the translocation, researchers can determine which genes are physically interrupted or relocated, providing strong clues about the location and identity of the disease-causing gene.

Question 12

Genes for regulatory elements, such as creb, were found to be important in animal learning. Which of the following would increase the probability that such an element is studied throughout the animal kingdom?

Accepted Answer

The finding that creb is highly conserved would increase the probability that it is studied throughout the animal kingdom because it suggests that the gene is important and necessary for basic biological processes. Conserved genes are generally considered to be ancient, essential and typically have been maintained throughout evolution because of their vital role in enabling life.

Question 13

In a disease associated with a nucleotide repeat, anticipation is often noticed in subsequent generations, usually associated with a more severe phenotype. Which of the following is a more likely cause of anticipation?

Accepted Answer

Nucleotide repeat diseases, such as Huntington's disease, are caused by unstable CAG repeats, which tend to expand in size from one generation to the next, resulting in a more severe phenotype. This is known as anticipation, and it is thought to be caused by the increased instability of the CAG repeat alleles with higher numbers of repeats. Subtle phenotypic nuances (B) or exposure to mutagens (C) are not likely causes of anticipation, and there is no evidence to suggest that highly repeated sequences (D) are expressed more often or that the sequences become more stable (E) in later generations.

Question 14

In Drosophila, mutation screening usually involves use of a balancer chromosome that includes three elements: a set of overlapping inversions, an easily recognized dominant mutation, and a recessive lethal mutation that prevents balancer homozygotes from surviving. Which one, or combination, of these elements is necessary and sufficient to suppress crossovers?

Accepted Answer

The overlapping inversions on the balancer chromosome are necessary and sufficient to suppress crossovers. This is because inversions disrupt the pairing and recombination of homologous chromosomes during meiosis, preventing crossing over between the balancer chromosome and the wild-type chromosome. The dominant mutation and recessive lethal mutation on the balancer chromosome are used to easily identify and select for balancer-containing progeny, but they are not directly involved in suppressing crossovers.

Question 15

A researcher wants to mutagenize an organism. He is not in need of a large number of mutants but is more concerned with being able to find and then to amplify the mutated sequence. Which of the following would therefore be more useful?

Accepted Answer

Transposon insertion is useful because it allows for easy identification and amplification of the mutated sequence due to the known sequence of the transposon, which can be used as a tag.

Question 16

The reasons for using transposon-based mutagenesis include all of the following except __________.

Accepted Answer

Transposon-based mutagenesis does not involve addition of alkyl groups to bases. The other options are valid reasons for using transposon-based mutagenesis.

Question 17

If you wish to rid an experimental organism of the function of a gene, you can use RNAi. What would you inject into the organism?

Accepted Answer

dsRNA homologous to the gene is the best choice for RNA interference (RNAi). This dsRNA will be processed into small interfering RNAs (siRNAs) that are complementary to the mRNA transcript of the targeted gene. The siRNAs will then associate with other proteins to form the RNA-induced silencing complex (RISC) that will cleave the mRNA transcript, effectively silencing the expression of the target gene.

Question 18

Conditional alleles result in phenotypic differences in permissive as opposed to restrictive conditions. What do these conditions have in common?

Accepted Answer

The answer of Conditional alleles result in phenotypic differences in...

Question 19

EMS (ethylmethane sulfonate)is mutagenic because __________.

Accepted Answer

EMS adds alkyl groups to bases, causing them to mispair during replication, leading to mutations.

Question 20

In reverse genetics, what is the correct order in which the experimenter proceeds?

Accepted Answer

In reverse genetics, the process typically involves inducing a mutation in a gene with a known sequence and then screening for phenotypic changes to understand the gene's function.

Quiz 16: Forward Genetics and Recombinant Dna Technology